Tata Institute of Fundamental Research Hyderabad, Hyderabad, India.
FEBS J. 2019 Dec;286(23):4737-4753. doi: 10.1111/febs.14988. Epub 2019 Jul 19.
Although the interaction of apoE isoforms with amyloid-β (Aβ) peptides plays a critical role in the progression of Alzheimer's disease, how they interact with each other remains poorly understood. Here, we investigate the molecular mechanism of apoE-Aβ interactions by comparing the effects of the different domains of apoE on Aβ. The kinetics of aggregation of Aβ1-42 are delayed dramatically in the presence of substoichiometric, nanomolar concentrations of N-terminal fragment (NTF), C-terminal fragment (CTF) and full-length apoE both in lipid-free and in lipidated forms. However, interactions between apoE and Aβ as measured by intermolecular Förster resonance energy transfer (FRET) analysis were found to be minimal at t = 0 but to increase in a time-dependent manner. Thus, apoE must interact with one or more 'intermediates' rather than the monomers of Aβ. Kinetics of FRET between full-length apoE4 labelled with EDANS at position 62 or 139 or 210 or 247 or 276, and tetramethylrhodamine-labelled Aβ (TMR-Aβ), further support an involvement of all the three domains of apoE in the interactions. However, the above-mentioned residues do not appear to form a single pocket in the 3-dimensional structure of apoE. A competitive binding assay examining the effects of unlabelled fragments or full-length apoE on the FRET between EDANS-apoE and TMR-Aβ show that binding affinity of the full-length apoE to Aβ is much higher than that of the fragments. Furthermore, apoE4 is found to interact more strongly than apoE3. We hypothesize that high affinity of the apoE-Aβ interaction is attained due to multivalent binding mediated by multiple interactions between oligomeric Aβ and full-length apoE.
虽然载脂蛋白 E 异构体与淀粉样蛋白-β（Aβ）肽的相互作用在阿尔茨海默病的进展中起着关键作用，但它们如何相互作用仍知之甚少。在这里，我们通过比较载脂蛋白 E 的不同结构域对 Aβ 的影响来研究载脂蛋白 E-Aβ 相互作用的分子机制。在无脂质和脂质化形式下，亚化学计量的纳米摩尔浓度的 N 端片段（NTF）、C 端片段（CTF）和全长载脂蛋白 E 均能显著延迟 Aβ1-42 的聚集动力学。然而，通过分子间Förster 共振能量转移（FRET）分析发现，载脂蛋白 E 与 Aβ 的相互作用在 t=0 时最小，但随着时间的推移呈时间依赖性增加。因此，载脂蛋白 E 必须与一个或多个“中间体”相互作用，而不是与 Aβ 的单体相互作用。用 EDANS 在位置 62 或 139 或 210 或 247 或 276 标记全长载脂蛋白 E4 与四甲基罗丹明标记的 Aβ（TMR-Aβ）之间的 FRET 动力学进一步支持载脂蛋白 E 的所有三个结构域都参与了相互作用。然而，上述残基在载脂蛋白 E 的三维结构中似乎没有形成一个单一的口袋。竞争结合测定法研究了未标记片段或全长载脂蛋白 E 对 EDANS-载脂蛋白 E 和 TMR-Aβ 之间 FRET 的影响，结果表明全长载脂蛋白 E 与 Aβ 的结合亲和力远高于片段。此外，发现载脂蛋白 E4 比载脂蛋白 E3 相互作用更强。我们假设，由于寡聚 Aβ 与全长载脂蛋白 E 之间的多种相互作用介导的多价结合，实现了载脂蛋白 E-Aβ 相互作用的高亲和力。
